'\" t
.\"     Title: subgid
.\"    Author: Eric Biederman
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: 22/07/2021
.\"    Manual: Formats et conversions de fichiers
.\"    Source: shadow-utils 4.9
.\"  Language: French
.\"
.TH "SUBGID" "5" "22/07/2021" "shadow\-utils 4\&.9" "Formats et conversions de fich"
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.SH "NOM"
subgid \- the configuration for subordinate group ids
.SH "DESCRIPTION"
.PP
Subgid authorizes a group id to map ranges of group ids from its namespace into child namespaces\&.
.PP
The delegation of the subordinate gids can be configured via the
\fIsubid\fR
field in
/etc/nsswitch\&.conf
file\&. Only one value can be set as the delegation source\&. Setting this field to
\fIfiles\fR
configures the delegation of gids to
/etc/subgid\&. Setting any other value treats the delegation as a plugin following with a name of the form
\fIlibsubid_$value\&.so\fR\&. If the value or plugin is missing, then the subordinate gid delegation falls back to
\fIfiles\fR\&.
.PP
Note, that
\fBgroupadd\fR
will only create entries in
/etc/subgid
if subid delegation is managed via subid files\&.
.SH "LOCAL SUBORDINATE DELEGATION"
.PP
Each line in
/etc/subgid
contains a user name and a range of subordinate group ids that user is allowed to use\&. This is specified with three fields delimited by colons (\(Fo\ \&:\ \&\(Fc)\&. These fields are:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
login name or UID
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
numerical subordinate group ID
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
numerical subordinate group ID count
.RE
.PP
This file specifies the group IDs that ordinary users can use, with the
\fBnewgidmap\fR
command, to configure gid mapping in a user namespace\&.
.PP
Multiple ranges may be specified per user\&.
.PP
When large number of entries (10000\-100000 or more) are defined in
/etc/subgid, parsing performance penalty will become noticeable\&. In this case it is recommended to use UIDs instead of login names\&. Benchmarks have shown speed\-ups up to 20x\&.
.SH "FICHIERS"
.PP
/etc/subgid
.RS 4
IDs des groupes subalternes d\*(Aqun utilisateur\&.
.RE
.PP
/etc/subgid\-
.RS 4
Backup file for /etc/subgid\&.
.RE
.SH "VOIR AUSSI"
.PP
\fBlogin.defs\fR(5),
\fBnewgidmap\fR(1),
\fBnewuidmap\fR(1),
\fBnewusers\fR(8),
\fBsubuid\fR(5),
\fBuseradd\fR(8),
\fBuserdel\fR(8),
\fBusermod\fR(8),
\fBuser_namespaces\fR(7)\&.
